Dummy load

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alfaeire
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Re: RE: Re: Dummy load

Post by alfaeire » Fri Apr 02, 2021 1:58 am


sinus trouble wrote:No! Resistors in parallel will reduce in Ohmic value but double in power (Watts)

Resistor in series will increase in Ohmic value but will remain the equivalent of one resistor in terms of power.

Haha! Get some Kip and worry about it another day!
I've cancelled the order,
I should have ordered 100ohm resistors instead of 50ohm, put in parallel they will reduce, that's the first issue.

The second issue is shitty sleep patterns and lockdown buys are not a good idea

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Re: Dummy load

Post by sinus trouble » Fri Apr 02, 2021 2:05 am

Zozo wrote:
Fri Apr 02, 2021 1:49 am
sinus trouble wrote:
Thu Apr 01, 2021 11:45 pm
Dummy03.png
Very nice Sinus. I like the build quality :tup
Cheers Zozo! :)

It took some serious heat to get them little F*ckerz soldered! :lol: Hopefully the orientation and volume of the can will help convection and cooling?

Im not sure which route i will take with the sampling? But its there to experiment with!
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Re: Dummy load

Post by Zozo » Fri Apr 02, 2021 2:10 am

sinus trouble wrote:
Fri Apr 02, 2021 2:05 am
Zozo wrote:
Fri Apr 02, 2021 1:49 am
sinus trouble wrote:
Thu Apr 01, 2021 11:45 pm
Dummy03.png
Very nice Sinus. I like the build quality :tup
Cheers Zozo! :)

It took some serious heat to get them little F*ckerz soldered! :lol: Hopefully the orientation and volume of the can will help convection and cooling?

Im not sure which route i will take with the sampling? But its there to experiment with!
High Voltage 1pF capacitor with 50 ohm match shunting resistors, useful for other alignment jobs. That's what I use for a Bi directional coupler I use... Hold up I'll find a picture.
20210111_132423.jpg
Obviously yours will be inside the dummy load and not external like this picture.
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Re: RE: Re: Dummy load

Post by sinus trouble » Fri Apr 02, 2021 2:10 am

alfaeire wrote:
Fri Apr 02, 2021 1:58 am
sinus trouble wrote:No! Resistors in parallel will reduce in Ohmic value but double in power (Watts)

Resistor in series will increase in Ohmic value but will remain the equivalent of one resistor in terms of power.

Haha! Get some Kip and worry about it another day!
I've cancelled the order,
I should have ordered 100ohm resistors instead of 50ohm, put in parallel they will reduce, that's the first issue.

The second issue is shitty sleep patterns and lockdown buys are not a good idea

Sent from my SM-A526B using Tapatalk
Haha! Yes a higher resistance will allow you to parallel more devices, Its all a learning curve and you will get there in the end! :)

Just takes time and patience! :)
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Re: Dummy load

Post by Zozo » Fri Apr 02, 2021 2:13 am

There's obviously an insertion loss which needs to be accounted for when aligning TX or RX equipment.

EDIT: above text is in regards to the last picture I posted.

Example of other uses.
bi-directinal-coupler.png
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alfaeire
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Re: Dummy load

Post by alfaeire » Fri Apr 02, 2021 3:12 am

250 Watts 100 Ohms
https://a.aliexpress.com/_m05SKkj

OK, bought 4 of these lads.
Now I wait.. And I might sleep.

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Re: Dummy load

Post by sinus trouble » Sat Apr 03, 2021 12:18 am

Zozo wrote:
Fri Apr 02, 2021 2:10 am
sinus trouble wrote:
Fri Apr 02, 2021 2:05 am
Zozo wrote:
Fri Apr 02, 2021 1:49 am


Very nice Sinus. I like the build quality :tup
Cheers Zozo! :)

It took some serious heat to get them little F*ckerz soldered! :lol: Hopefully the orientation and volume of the can will help convection and cooling?

Im not sure which route i will take with the sampling? But its there to experiment with!
High Voltage 1pF capacitor with 50 ohm match shunting resistors, useful for other alignment jobs. That's what I use for a Bi directional coupler I use... Hold up I'll find a picture.

20210111_132423.jpg

Obviously yours will be inside the dummy load and not external like this picture.
Nice neat sampler Zozo! :)

Yet still undecided on the sampler configuration? The feed through capacitor fitted has no value marking so will need testing! I suspect it is for DC filtering purpose? I would hazard a guess that it is in the low nF range?

It will most likely end as just a simple RF rectifier which can quickly be read using a multimeter?

Either way? It wont be to a calibrated standard :lol:
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Re: Dummy load

Post by Zozo » Sat Apr 03, 2021 12:34 am

Yes just rectifying the signal to DC is very good way of measuring RF power. For most jobs my AV-201 is good enough for what I do. I know it's most accurate in the 5W scale and the readings get worse, i.e. +/- a certain percentage in the higher ranges.

I've never needed to have a super accurate meter, just a general idea is good enough for me ;)
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Re: Dummy load

Post by sinus trouble » Sat Apr 03, 2021 1:01 am

Totally agree Zozo! :)

I have the Daiwa CN-801 which is close enough for me for measurements.

I absolutely love my oscilloscope! It has helped me diagnose so many faults and i simply could not do without it! However it is basic and struggles at higher frequencies!

The wave forms are clear but the roll off prevents any accurate measurement.

I am hoping to treat myself to an upgrade soon, The price tag will most likely be a hefty one? But worth every penny! :)
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Re: Dummy load

Post by sinus trouble » Mon Apr 05, 2021 11:04 pm

Although its not really necessary, I have done a quick model of a sampler in LTSpice

It is the simplest version with just a coupling capacitor suitable for connecting to an oscilloscope etc..

It is approximately a 10:1 ratio and phase shift is virtually non existent?

the 1Meg/1n RC circuit is a rough representation of the test probe connected.

Diode rectifier version to follow!
Dummy Sampler.PNG
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Re: Dummy load

Post by sinus trouble » Mon Apr 05, 2021 11:27 pm

Here is the very basic rectified version for simple multimeter tests.

Both versions are not high precision and will depend on frequency and loading

If anyone can see any improvements (Or cockups) feel free to comment :lol:
Dummy Detector Diode.PNG
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Re: Dummy load

Post by Zozo » Mon Apr 05, 2021 11:32 pm

Looking good Sinus, being able to sample a signal without damaging your test equipment is a very useful bit of kit. Are you going to build one as a separate adapter, or is it all going inside the dummy load? I can't see anything wrong with what you have presented.

I was trying to find a program for simulating a circuit, and came across something about LTSpice. But I haven't tried it yet.
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Re: Dummy load

Post by sinus trouble » Mon Apr 05, 2021 11:54 pm

Cheers Zozo! :)

Hopefully i can squeeze it into the dummy load, I doubt the oil will cause any harm?

LTSpice is one of those programs that 'Real' Engineers would sneer at in disgust! I agree in some sense!

However it is free and pretty adaptable! I have simulated various filters, oscillators, mixers etc... and its damn close for such a basic program! Deffo worth a try! :)
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Re: Dummy load

Post by Zozo » Tue Apr 06, 2021 12:14 am

Cheers Sinus, I'll give it a try. I have been playing around with another bit of software all afternoon that BTon-FM mentioned to me for designing Meander coils on PCB's, which I think I've got the hang of.

Yes I think putting it all inside the dummy load should be fine. I'm sure I've seen that done before by others.
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Re: Dummy load

Post by radium98 » Tue Apr 06, 2021 6:03 pm

maybe better to fit if you can find germanium diode ?

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Re: Dummy load

Post by Albert H » Wed Apr 07, 2021 12:51 am

Germanium might be a bit fragile. Go for a Schottky diode instead.
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Re: Dummy load

Post by sinus trouble » Wed Apr 07, 2021 1:07 am

I have now completed the Dummy load :)

Gonna perform a burn in test @ 60watts hopefully over the weekend?

I substituted the 100pf decoupling cap for a 1.8pf and tested the actual capacitance of the feed through cap which turns out to be 8nf as i expected to be between 1 - 10nf?

I performed a quick test @ 5watts! The SWR was around 1.2:1 and the measured DC sample voltage was 20V

@ Radium, I do have a bunch of random small signal diodes which i did consider but are too small for my eyes to read the part numbers! :lol:

Anyways below is a pic! :)
Dummy DC Sampler.png
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Re: Dummy load

Post by sinus trouble » Wed Apr 07, 2021 1:44 am

Albert H wrote:
Wed Apr 07, 2021 12:51 am
Germanium might be a bit fragile. Go for a Schottky diode instead.
As it happens? I do have some Schottky diodes which i used for SMPSU repairs but they are rather large?
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Re: Dummy load

Post by radium98 » Wed Apr 07, 2021 5:11 pm

coolllllllllll sinus , nowadays i have some sinus troubles tooo lol

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Re: Dummy load

Post by sinus trouble » Thu Apr 08, 2021 11:37 pm

radium98 wrote:
Wed Apr 07, 2021 5:11 pm
coolllllllllll sinus , nowadays i have some sinus troubles tooo lol
I do hope that you are referring to Sinusoidal difficulties and have no need to see a doctor! :lol:
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